The following Perl function uses the IO::Socket and Net::Nslookup perl modules (available on CPAN) to test a TCP socket connection from the machine running the script to a remote host. The function accepts either an ip address or a hostname. If a hostname is passed to the function it will first be resolved to an ip address, producing an error if the hostname is not resolveable.

This is a good replacement for those that rely on the telnet command to test for TCP port availability.

sub socketConnect(){
 #This function requires two arguments; a host and a TCP port. Example
+: socketConnect("server1","80");
 use IO::Socket;
 use Net::Nslookup;
 my ($peeraddr,$peerport) = @_;
 my $sock = new IO::Socket::INET ( Timeout => 5, PeerAddr => $peeraddr
+, PeerPort => $peerport, Proto => 'TCP' );
 
 if ($sock){ 
  if ( print $sock "HELO\n" ) {
   print "$peeraddr TCP/$peerport" . " connection allowed\n"; 
  }
  close($sock); 
 } else {
 #Socket open failed or could not resolve hostname
  if (nslookup $peeraddr){
   print "$peeraddr TCP/$peerport" . " connection refused\n";
  } else {
   print "Could not resolve $peeraddr\n";
  }
 }
}
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Source: ApplicationBistro.com